Market timing can be tricky and more often than not, individual investors have tended to come in late on the rally. With stocks at five-highs, it remains to be seen if the inflows (and the bull market) will continue.

Meanwhile, investors also plowed a huge sum into international stock market mutual funds. According to ICI, global equity funds raked in $6.8 billion during the first full week of 2013, the most since April 2012. Similar data from EPFR Global, a Boston-based firm that tracks fund flows, showed that emerging market funds in particular attracted investors at the start of the year.

The combined $14.8 billion that went into U.S. and global equity funds was also a record based on ICI's data.

Even with the threat of the bond bubble bursting this year, investors extended their strong love for bonds, adding nearly $10 billion to bond mutual funds during the first week, according to ICI. In 2012, investors flooded bond funds with more than $300 billion.

Hibah Yousuf is a reporter at CNNMoney, where she covers stocks, bonds, commodities and currencies trading across the globe, as well as corporate earnings and other markets-related news. Prior to joining the site in 2009, she interned at Money Magazine.